1. Field of the Invention
This invention pertains to the field of automatic shift manual transmissions and select shift manual transmissions, particularly to the types of these transmissions applicable to motor vehicles.
2. Description of the Prior Art
Automatic transmissions for transmitting power between an input and an output, either over a continuously variable range of speed ratios or in discrete step changes among speed ratios, have associated with them several sources of parasitic losses, which adversely affect fuel economy. These losses are associated with a torque converter, open hydraulic friction clutches and brakes, hydraulic pump, and gear meshes.
To improve fuel economy in a motor vehicle having an automatic transmission, an automated shift manual (ASM) transmission can be used to eliminate or substantially reduce all of these parasitic losses except gear mesh losses. An ASM transmission generally performs gear ratio changes by first interrupting torque transmitted from the engine to the transmission input, preparing the transmission components associated with the next speed ratio, and then restoring torque. A primary functional feature of ASM transmissions is the need to interrupt power transmitted from the engine to the transmission input shaft before or during each gear ratio change. This requirement can result in low quality gear ratio changes, which a vehicle operator or passenger may sense as noise, vibration and harshness.
A transmission operating in accordance with the present invention avoids entirely any interruption of power during gear ratio changes and avoids the inherent shift quality problems of ASMS. This invention, however, also reduces the magnitude of parasitic losses inherent in the operation of an automatic transmission to a much lower magnitude than is present in a conventional ASM transmission.